Wireless Markup Language (WML) is a markup language that allows developers to create web pages for mobile phones and other wireless devices. WML is based on XML and HTML, but it has some features and limitations that make it suitable for the wireless environment.
In this blog post, we will introduce WML, explain its basic syntax and structure, and show some examples of how to use it to create simple web applications.
What is WML?
WML stands for Wireless Markup Language. It is a markup language that is used to create web pages for mobile phones and other wireless devices that support the Wireless Application Protocol (WAP).
WAP is a set of standards that define how wireless devices can communicate with web servers and access web content. WAP uses a special protocol called Wireless Session Protocol (WSP) to transfer data between the device and the server. WSP is optimized for low bandwidth and high latency connections, and it compresses the data to reduce the amount of bytes transferred.
WML is one of the formats that WSP can use to deliver web content to the device. WML is designed to fit the constraints of wireless devices, such as small display screens, limited memory, low bandwidth, and simple user interfaces. WML allows developers to create web pages that are concise, monochromatic, and interactive.
How does WML work?
WML works with the concept of a deck and card metaphor. A WML document is composed of one or more cards, which are like pages in a website. Each card contains some content and some elements that define how the content can be displayed and interacted with by the user.
A WML document is also called a deck, and it has a unique URL that identifies it. A deck can contain multiple cards, but only one card can be displayed at a time on the device screen. The user can navigate between cards using links or buttons, or by using the device keys or voice commands.
A WML deck is delivered to the device as an XML document, which is parsed by a WML browser or interpreter. The WML browser renders the content of the current card on the screen, and handles the user input and navigation events.
WML Syntax and Structure
WML is an XML-based markup language, which means that it follows some rules for writing well-formed XML documents. Some of these rules are:
- A WML document must start with an XML declaration that specifies the XML version and encoding.
- A WML document must have a document type declaration (DOCTYPE) that references the WML DTD (Document Type Definition), which defines the valid elements and attributes of WML.
- A WML document must have a root element named <wml>, which contains all the other elements of the document.
- A WML document must have one or more <card> elements, which represent the cards of the deck. Each card must have an id attribute that uniquely identifies it within the deck, and a title attribute that specifies its name.
- A WML document can have other elements that provide additional functionality, such as <do>, <go>, <p>, <select>, <input>, <timer>, <var>, etc. These elements will be explained later in this post.
- A WML document must use tags and attributes in lowercase letters, and must enclose attribute values in quotation marks.
- A WML document must close all tags properly, either by using an end tag (</tag>) or by using a self-closing tag (<tag/>).
- A WML document must escape some special characters using entities, such as & for &, < for <, > for >, etc.
Here is an example of a simple WML document that contains two cards: